Thermoplastic resin films are used as household cling wraps to contain food and other items by clinging to one or more surfaces of the container in which the food is housed or to itself to thereby provide a seal which reduces the degree of exposure of the contents of the container to the environment. A necessary characteristic of such film wrap is the ability to "cling", that is, to adhere to itself or to form a tight seal with other surfaces, as when the film is used as a cover for containers. These films can be employed to preserve the freshness and moisture content of wrapped food items and to prevent the migration of food odors.
Thermoplastic resin films do not generally possess inherent cling characteristics sufficient to adhere satisfactorily to themselves and other surfaces. The cling characteristic of thermoplastic films is generally obtained through the use of so-called cling agents or adhesives. Adhesives are chosen for their ability to produce a surface on a thermoplastic film that can be sealed, opened and resealed, and are selected with due care in consideration of the use of thermoplastic films in direct food contact applications.
A balance must be attained between the film's "cling" and "handling" or "handleability" characteristics. "Handleability" is the characteristic of the film to resist inadvertent clinging to itself and to other surfaces during use. While cling agents impart good cling properties to the film, it has generally been observed that an increase in the amount of adhesives incorporated into the film to enhance the cling provides a corresponding decrease in the handleability of the film. With an increased adhesive amount, the tendency of the film to inadvertently adhere to itself and to other surfaces increases. One type of inadvertent sticking is known as premature sticking, that is, before the adhesive coated film can be properly positioned over a target surface, inadvertent contact of the adhesive with the target surface or the cling wrap itself causes premature sticking at one or more positions, thereby inhibiting proper positioning of the cling wrap for use. Moreover, with the increased use of microwave ovens, it has become desirable for food cling wraps to be used in microwave re-heating applications.
Embossed films are well known in the art. For instance, U.S. Pat. No. 5,662,758 to Hamilton, et al., ("Hamilton") describes a method for making a flexible film having pressure sensitive adhesive protected from inadvertent adherence. The method coats a forming screen with an interconnected layer of pressure sensitive adhesive and places a piece of flexible film in contact with the layer of adhesive. The layer of adhesive preferentially adheres to the piece of flexible film. The forming screen has a plurality of recesses therein. The coating step applies the layer of adhesive without bridging the recesses. Another step forms the flexible film to create a plurality of protrusions that are registered with the interconnected layer of pressure sensitive adhesive by virtue of using the same screen to transfer adhesive and to form the protrusions. The forming screen may be wrapped around a rotating drum and the piece of flexible film may be a portion of a continuous web of flexible film. The adhesive in Hamilton only covers the raised surfaces.